The present invention generally relates to separating method and apparatus and, in particular, to methods and apparatus for minimizing fringing of a protective layer when separated from an image-bearing medium.
Recent developments in the image forming arts use thermal imaging laminates for achieving high quality, high resolution images, such as for graphic arts and radiological images. Examples of such medium are described in commonly-assigned International Patent Application No. PCT/US 87/03249 published Jun. 16, 1988, under International Publication No. WO 88/04327; and U.S. Pat. No. 5,200,297. The medium is a laminate in which an image forming layer thereof is a porous or particulate imaging material, preferably, a layer of carbon black that is deposited on a heat-activatable image-forming surface of a first sheet-like element. The image forming layer has an adhesive strength to a first sheet-like element of the laminate that is a function of its exposed state. The first sheet-like element carrying the imaging material is covered with a second sheet-like element that is laminated to the first so that the imaging material is confined between the first and second sheets.
This medium can be imagewise exposed as by laser scanning, whereby exposed portions of the imaging material are firmly attached to the first sheet, and unexposed portions of the imaging material are firmly attached to the second sheet. The result is a first image surface which comprises exposed portions of an image-forming substance that is more firmly attached to the first sheet and a complementary second image surface which comprises non-exposed portions of the image-forming substance carried or transferred thereto.
After imaging in the manner noted, the sheets are then peeled, separated or delaminated with the first or image-bearing sheet carrying exposed imaging material portions, and the second element carrying unexposed portions. As a result of the peeling, a pair of complementary or binary image layers is obtained, either one of which may for reasons of informational content be considered the principal image area. Such image forming materials and processes are capable of producing extremely high quality and high resolution images.
However, there are possibilities for damaging the image layer by physical contact, physical elements or the like. Therefore, it is desirable to protect the image forming layer. One known approach is through the application of a protective overcoating material, e.g., a thin, transparent, but durable/protective layer, such as described in International Patent Application No. PCT/US91/08345 (Publication No. WO 92/09930) (Fehervari et al.); and pending U.S. application Ser. No. 08/065345 (Bloom et al.). Lamination of protective overcoats, such as those described in the cited patent applications, have been accomplished by using a continuous roll, i.e. carrier web, to transfer the durable protective layer to the image carrying sheets. Activation energy is necessary for fusing the durable layer to the imaged sheet at a nip formed by and between a pair of compression rollers.
While such laminating approaches for protecting the image-bearing media are successful, nevertheless possibilities exist that during this process artifacts, such as edge fringing, might occur adjacent to punch holes formed in the laminated image-bearing medium; as well as leading and trailing edges of such medium. Fringing is considered to be stringy fragments of the protective layer which are not completely removed from the edges, such as punch holes in the image-bearing sheet during separation of the carrier from the keeper sheet. In addition, such fragments if they become separated from the image-bearing sheet and/or the carrier web may fall onto other image-bearing media so as to cause artifacts on these other sheets.
Accordingly, there is a continuing desire for improving upon efforts for enhancing the protection of the image-bearing sheet by reducing the formation of undesirable fringing of the protective layer in punch holes formed in the image-bearing sheet which might adversely affect image quality.
In accordance with the present invention there are provided improved methods and apparatus for minimizing the problems noted above in separating a carrier web having a protective layer thereon from a keeper sheet of image-bearing media. In this regard, provision is made for a method of separating unused portions of a protective layer from and adjacent edges of a keeper sheet of image-bearing medium comprising the steps of: directing the medium through a nip between a peel means and a constraining means, peeling the carrier web and the unused protective layer about the peel means and away from and off the keeper sheet as the keeper sheet advances downstream over the constraining means, and applying tension to the protective layer bearing surface adjacent the edges of the keeper sheet at or downstream of the peel means.
In an illustrated embodiment, the method is achieved by having the constraining means induce a bending of at least a cantilevered portion of the protective layer on the keeper sheet downstream of the peel means to thereby induce the tensioning of portions of the protective layer bearing surface adjacent the edges of the keeper sheet.
In another illustrated embodiment the method includes the step of using a compliant surface on at least one of the constraining means or peel means at the nip. Further in this connection, there is provided a constraining member whose surface portions are made from a compliant material. Still further, the peeling means includes a peeling surface with a compliant material thereon for engaging the carrier web.
In still another illustrated embodiment, the method includes applying tension to the keeper sheet at or downstream of the peel means in an amount which forces an unused portion of the protective layer adjacent to any edge of the keeper to be moved off of and away from the keeper sheet, and which further does not remove such protective layer portions from the carrier web.
In an embodiment, there is provided an apparatus for separating a carrier web having a protective layer from a keeper sheet of image-bearing medium. The apparatus comprises in combination, a first means and peeling means which are operable for forming a nip therebetween for receiving a sheet of image-bearing medium. The peeling means has a peeling surface about which the carrier web and unused portions of the protective layer are peeled off the keeper sheet, and a second mechanism or means being operable for inducing tension in the protective layer at or downstream of the nip for separating the protective layer from edges of the keeper sheet.
In another illustrated embodiment, provision is made for apparatus for separating an image bearing medium from a carrier web and a protective layer thereon. The apparatus, comprises in combination, a constraining means and peeling means which are operable for forming a nip therebetween for receiving a sheet of image-bearing medium. The peeling means has a peeling surface about which the carrier web and unused protective layer are peeled off the keeper sheet. The constraining means bends the keeper sheet and the protective layer so as to place the protective layer bearing surface in tension at or downstream of the peeling surface for insuring clean separation of the unused protective layer from the keeper sheet particularly at the edges.
In other illustrated embodiments, provision is made for compliant material being on at least one of the peeling means or constraining means in the nip. In one example, the peeling means includes a surface having a compliant material engageable with the protective layer. While in another example, the compliant material is on the constraining means for engaging the keeper sheet.
In yet another illustrated embodiment, the apparatus includes a deflector roll located downstream of the constraining means for engaging and deflecting the keeper sheet.
An object of the present invention is to provide novel methods and apparatus for separating appropriate or unused portions of the protective layer from a keeper sheet of image-bearing medium to obtain complete removal of the unused portions of the protective layer from the edges of the keeper sheet. Included herein are the provisions of such methods and apparatus which may be applied to any of the edges of the image-bearing medium to avoid the problems of fringing at such edges as the unused portions of the protective layer at the edges are removed from the keeper sheet. These edges include exterior edges, such as leading and trailing edges as well as internal edges, such as edges which define a punch hole or the like. In this regard, the carrier web and the unused portions of the protective layer are pulled or peeled off and away from the keeper sheet at its edges.
Another object of the present invention is to provide an improved image-bearing medium or keeper sheet produced through an improved process and apparatus which substantially reduces, if not avoids the problem of fringing of the unused portions of the protective layer from edges on the keeper.
Another object is to insure that the unused protective layer material which is separated from the keeper sheet edges remains with the separated carrier web for waste removal purposes.